In an optical lithography step upon manufacturing a semiconductor device, a so-called blurred state occurs if a focus position of an exposure apparatus is not suitably set in a case of forming a circuit pattern. In this case, a desired circuit pattern cannot be formed on a semiconductor substrate. Due to this, accompanying refinement of a circuit pattern used for the semiconductor device, focus accuracy in the exposure apparatus is becoming one of the most important factors.
In an exposure apparatus that uses ArF with alight source wavelength of 193 nm or a KrF excimer laser with that of 248 nm, a plurality of permeating portions having a phase difference is provided on a photo mask, and the focus position was measured by using the phase difference.
However, an EUV (Extreme Ultraviolet) exposure apparatus of which development is under progress as a next generation exposure apparatus has a very short light source wavelength of 13.5 nm. Due to this, in order to provide the phase difference necessary for measuring the focus position, a step amount of a step to be provided on the photo mask becomes 3 nm, which is very small. Accordingly, it is difficult to obtain sufficient processing accuracy for the step to be provided on the photo mask.
Further, there is a method that measures the focus position by using a non-telecentric lighting. In this method, since the number of openings in a projection lens of the EUV exposure apparatus is small, only about 1 nm of dislocated amount can be observed relative to 10 nm of focus change. Due to this, sufficient inspection performance for the focus position cannot be obtained.
Accordingly, in a case where the inspection performance of the focus position is low, the desired circuit pattern cannot be formed on the semiconductor substrate, thus it is desired to accurately measure the focus position.